Hey guys, my name is Holderik and I play on EUNE. I played as ADC at first but I hated relying on my support so I decided to play MID. I started maining Malzahar in S5 even before he was reworked and since he got some mini reworks too.
Hope you enjoy my guide and feel free to leave comment or your questions.

Malzahar is a mid range control mage with good CC but hes kit is a not a burst type like Syndras but a DOT type.
When I first tried him I saw the huge 1v1 potential in him and I thought he could be good in soloq and he was. After playing this seasons(8.) 10 placement game I had 8w-1l with him on mid lane . I used to play him as a support but after his W changes i don't think he is that effective.

+ huge 1v1 potential especially with his R
+ safe pick, hardly has any hard matchups
+ really good pusher

- medium range
- his R can be cancelled or countered with QSS
- no escape in his kit
- rely on frontlane(if he has to frontlane he R 100% will be cancelled and he's dead)

I tried different runes on him and Unsealed Spellbook can be good expecially in higher elo. The lower cooldown on flash can have a big inpact on the game if you can gank/catch someone with your team or even alone. Also it has the higher pick rate.
I always use Summon Aery though. If I E on the enemy and then I reset my E with my Q Aery damages twice while I keep autoing the enemy and don't forget about your W. This combo can do a lot of damage early and if you have ignite its almost 100% a first blood or at least a kill.

Passive - Void Shift: If you hasn't taken damage recently you get a shield that greatly reduces the damage from the first attack that hits you and while shielded you can't be CCd(stun,root,snare,etc.).

Q - Call of the Void: Your Q is a skillshot that creates two orbs and after a short duration damages and silences everything in between them. At max rank it silences for 2 seconds and if you use Q on a target that has your E on them it resets your E.

W - Void Swarm: Summon Voidllings that attack nearby enemies prioritizing targets that has your E on them. Your voidllings also deal more damage to Ed targets and move faster into their direction. After the nerfs and changes your Voidllings are one shoted with auto attacks but they stronger against minions.

E - Malefic Visions: Cast a damage over time spell on an enemy target. If your target is hit by your Q or R the timer of your E is reseting. When it kills a target it spreads to another target it refunds some mana. Thats your main source of damage and you can clear waves extremely fast with your E + W.

R - Nether Grasp: It's a pont click ability and after casting it your target can't move or use spells for 2,5 seconds. This ability is your only hard CC besides your silence and you can melt mages with it but it has some health ratio against tanks as well. Cleanse can't used by your target but QSS can cancel the CC.